Afferent input is critically important for normal development of central auditory nuclei. This project will assess the capacity of a cochlear prosthesis to provide such input in a congenitally deaf animal model. The proposed series of studies will compare morphometric and physiologic changes in the central auditory tract in deaf Dalmatians stimulated with a multichannel cochlear prosthesis with similar measures in untreated deaf and hearing Dalmatians of similar age. These studies will extend current work on changes in the peripheral auditory tract of the deaf Dalmatian. The rationale for these studies is based on 1) observations that auditory deprivation induces measurable changes in the volume of defined cell regions of central auditory nuclei and cell size, 2) auditory tract pathologic changes exhibited by the deaf Dalmatian that suggest it to be an especially appropriate model of congenital human deafness, and 3) early studies that suggest that electrical stimulation may exert a trophic effect on neurons of the peripheral auditory tract. It is anticipated that results from these studies will provide fundamental neuroanatomic information crucial to understanding the effects of prosthetic intervention in early human deafness. These studies are the focus of this 5 year Clinician Investigator Development Award application. Extended g in morphometric, electrophysiologic and statistical analysis will be organized around the proposed project. This training will be used to provide a basic framework that will complement a comprehensive neurotologic program of study of early sensorineural hearing loss and its treatment.